Universal Serial Bus (USB) compatible devices have become ubiquitous the past several years. Portable and desktop computers may include several USB ports or connectors. Other connectors, such as the Lightning™ connector, may include USB functionality. USB type C connectors are the latest to be developed and can now be found on many devices.
USB type C connectors may include rotatable connector inserts which may be plugged into a corresponding connector receptacle in either of two orientations 180 degrees apart. To detect which orientation has been used, a USB type C connector receptacle may include two connection detect pins, referred to as CC1 and CC2 pins. After a connection between devices is made using a cable, one of the CC pins may be used by a connector receptacle to provide power to a dongle or active cable. This pin may be referred to as a VCONN pin. The remaining CC pin may be used to detect a connection and its orientation and as a signaling path between devices, and may be referred to here as a CC signaling pin.
For example, connector receptacles on communicating devices may each include two CC connection detect pins. Connector inserts on a cable may each include one connection detection pin that are connected together by a conductor in the cable. In this way, a connection detection pin on one device may connect to one connection detection pin on a second device. This connection detection may then be used to determine that a connection between communicating devices has been made, and which of the communicating devices may provide power and which may receive power. This connection may then be used as a signaling pin to transfer data between the devices. Signals on this pin may be relatively low-speed, single-ended data signals. The remaining connection detection pins, the VCONN pins on the connector receptacles, may be used to provide power to connector inserts for dongles and active cables.
Several factors may hinder data transmission over the CC connection detection pins used as signaling pins. For example, a device may either provide power or receive power over a VBUS line. Depending on whether the device provides or receives power, a ground drop at a receiver may shift or drift many hundreds of millivolts in opposite directions. Also, the power provided may start, stop, or change at various times, thereby changing the amount of ground shift or drift over time. This may render a simple bits-slice data receiver to be severely error-prone and non-functional in extreme cases. Also, high-frequency coupling from other signals on the connector, such as USB2 signals, may inject high-frequency noise on a signal being received at a CC signaling pin. Inductive coupling from other conductors, such as the VBUS power supply, may further degrade a received signal. These factors may complicate data reception at a CC signaling pin.
Thus, what is needed are circuits, methods, and apparatus that may reconstruct a data signal in the presence of ground drift, high-frequency signal coupling from other signals, and inductive coupling from power supplies and other signals.